Modelling and Realization of Pneumatics based Wall Climbing Robot for Inspection Applications

Climbing robots are highly in need for catering the inspection of the high rise buildings. Climbing Robots has to work in challenging environments and has to maneuver vertically against gravity and orient towards the specified target by adapting to various surfaces. The proposed Wall Climbing Robot weighs 1 Kg , works with four active suction cups and driven with pneumatic supply cylinder drive assembly. The robot moves by absolute holding of two suction cups at any instance and remaining two cups are allowed free to enable forward movement of the robot. The robot consists of vacuum generator, suction cup, pneumatic driven traverse assembly, controller and wireless high resolution camera. The designed robot is highly suitable for the continuous monitoring and inspection of high rise buildings. The vacuum generator is externally positioned and suction is derived through pneumatic supply hose. The developed robot climbs on the vertical wall at a velocity of 1.5 cm/s. Keyword –Wall climbing robot, suction cup, smooth surface, pneumatic operation, programmable logic controller


II. WALL CLIMBING ROBOT -SYSTEM ARCHITECTURE
The building blocks of the proposed climbing robot consists of electrical assembly, pneumatic assembly and mechanical assembly. The system block diagram is shown in Fig.1. The robot attachment to the wall and traverse on the wall is controlled by the four output relays.    Considering the Force balance, X axis:

Compressor
Since the robot functions with two front suction cups and two rear suction cups, 2 f N and 2 r N are considered in (1). Since the robot movement is achieved by holding and release of either the two front or two rear suction cups at any instant of time, 2 s F appears in (1). Y axis: Using (1), (2) and (3) Obviously, from (5) and (6), it can be seen that

 
Obviously, from (7) and (8) The proposed robot holds with 2 suction cups at any instant, considering the safety factor the theoretical holding force of the robot will be S F = 2 4 . 5 2 5 N ( 2 . 5 K g f ) ( 9 ) It is observed that from (4), for preventing the robot from sliding off from the wall each suction cup should have a holding force of 8.175 N. The condition for the robot not to fall off from the wall can be estimated through (5), (6). Substituting the parameters of table 1 in (5), and assuming a fall off limit of zero reaction force on the suction cup ,

IV. SELECTION OF SUCTION CUP, VACUUM GENERATOR A. Selection of suction cup
The effective diameter of the suction cup determines its holding force. The required diameter d of the each suction cup can be determined by   (11), NSCPI 15 Vacuum Generator capable of ejecting 75 l/min is selected [15]. Fig.6 depicts the developed prototype wall climbing robot with inspection camera and accessories. The robot is tested in real time and capable to traverse without any slide or drop off .Though the weight of the robot proposed is limited to 1Kg, it can be enhanced by increasing the suction cup diameter and suction rate of the vacuum generator. Fig.7 helps to identify the safe working region of the robot. The plot of Eq. (4) represents the robot in holding condition and not allow to slide. The plot of Eq. (5) represents the robot in about to fall off condition and helps to estimate the minimum holding force of the suction cup.

VI. CONCLUSION
In this work the pneumatic based wall climbing robot is mathematically modelled and realized using suction cups, pneumatic driven traverse assembly, Programmable logic controller and wireless high resolution camera. This robot is designed for continuous monitoring and inspection applications of high rise buildings. It can be concluded that S F = 5.4 N, derived from Eq. (5) will be the minimum holding force for the single cup. Hence to operate the proposed robot in the safety region, a holding force for each cup is maintained at S F = 8.175 N. The robot is able to traverse at a speed of 1.5 cm/s. The limitations of the robot are single degree of traverse, slow travel time. This will be addressed in the future research and development of a wall climbing robot.